;; content-on-sx — Markdown import adapter (markdown text -> block document).
;;
;; A line-based parser, the inverse of markdown.sx's asMarkdown. Confined to the
;; adapter boundary: the core knows nothing about Markdown. Handles a leading
;; --- frontmatter block (key: value -> doc metadata), ATX headings (#..######),
;; fenced code (```lang), blockquotes (> ), unordered (- / * ) and ordered (1. )
;; lists, thematic breaks (--- / ***), pipe tables (header + --- separator +
;; body), and paragraphs (consecutive plain lines joined with a space). Block ids
;; are assigned sequentially b0,b1…
;;
;; Requires (loaded by harness): block.sx, doc.sx, table.sx (mk-table),
;; meta.sx (doc-with-meta); markdown.sx for the adapter's export side.

(define md/-id (fn (i) (str "b" i)))
(define md/-blank? (fn (s) (= s "")))
(define md/-hr? (fn (s) (if (= s "---") true (= s "***"))))

(define
  ct-in?
  (fn
    (x xs)
    (cond
      ((= (len xs) 0) false)
      ((= (first xs) x) true)
      (else (ct-in? x (rest xs))))))

(define
  ct-starts-with?
  (fn
    (s prefix)
    (and
      (>= (string-length s) (string-length prefix))
      (= (substring s 0 (string-length prefix)) prefix))))

(define
  md/-drop
  (fn (s prefix) (substring s (string-length prefix) (string-length s))))

(define
  md/-drop-n
  (fn
    (xs n)
    (if
      (= n 0)
      xs
      (if
        (= (len xs) 0)
        xs
        (md/-drop-n (rest xs) (- n 1))))))

(define
  md/-join-with
  (fn
    (sep parts)
    (cond
      ((= (len parts) 0) "")
      ((= (len parts) 1) (first parts))
      (else (str (first parts) sep (md/-join-with sep (rest parts)))))))
(define md/-join-sp (fn (parts) (md/-join-with " " parts)))
(define md/-join-nl (fn (parts) (md/-join-with (str "\n") parts)))

;; ── heading detection (leading #s then a space) ──
(define
  md/-hashes
  (fn
    (s n)
    (if
      (and
        (< n (string-length s))
        (= (substring s n (+ n 1)) "#"))
      (md/-hashes s (+ n 1))
      n)))
(define
  md/-heading?
  (fn
    (line)
    (let
      ((n (md/-hashes line 0)))
      (and
        (> n 0)
        (<= n 6)
        (> (string-length line) n)
        (= (substring line n (+ n 1)) " ")))))
(define
  md/-heading-block
  (fn
    (line i)
    (let
      ((n (md/-hashes line 0)))
      (mk-heading
        (md/-id i)
        n
        (substring line (+ n 1) (string-length line))))))

;; ── list detection ──
(define
  ct-digit?
  (fn (ch) (ct-in? ch (list "0" "1" "2" "3" "4" "5" "6" "7" "8" "9"))))
(define
  md/-digits
  (fn
    (s n)
    (if
      (and
        (< n (string-length s))
        (ct-digit? (substring s n (+ n 1))))
      (md/-digits s (+ n 1))
      n)))
(define
  md/-ol?
  (fn
    (line)
    (let
      ((n (md/-digits line 0)))
      (and
        (> n 0)
        (>= (string-length line) (+ n 2))
        (= (substring line n (+ n 2)) ". ")))))
(define
  md/-drop-ol
  (fn
    (line)
    (let
      ((n (md/-digits line 0)))
      (substring line (+ n 2) (string-length line)))))
(define
  md/-ul?
  (fn
    (line)
    (if (ct-starts-with? line "- ") true (ct-starts-with? line "* "))))
(define
  md/-drop-ul
  (fn (line) (substring line 2 (string-length line))))

;; ── table detection ──
(define md/-pipe-row? (fn (line) (ct-starts-with? (trim line) "|")))
(define md/-sep-char? (fn (ch) (ct-in? ch (list "-" ":" "|" " "))))
(define
  md/-all-sep?
  (fn
    (s i)
    (if
      (>= i (string-length s))
      true
      (if
        (md/-sep-char? (substring s i (+ i 1)))
        (md/-all-sep? s (+ i 1))
        false))))
(define
  md/-has-dash?
  (fn
    (s i)
    (if
      (>= i (string-length s))
      false
      (if
        (= (substring s i (+ i 1)) "-")
        true
        (md/-has-dash? s (+ i 1))))))
(define
  md/-sep-row?
  (fn
    (line)
    (and
      (md/-pipe-row? line)
      (md/-all-sep? (trim line) 0)
      (md/-has-dash? line 0))))
(define
  md/-table-start?
  (fn
    (lines)
    (and
      (md/-pipe-row? (first lines))
      (> (len lines) 1)
      (md/-sep-row? (nth lines 1)))))
(define
  md/-strip-pipes
  (fn
    (s0)
    (let
      ((s (trim s0)))
      (let
        ((a (if (ct-starts-with? s "|") (substring s 1 (string-length s)) s)))
        (if
          (and
            (> (string-length a) 0)
            (=
              (substring
                a
                (- (string-length a) 1)
                (string-length a))
              "|"))
          (substring a 0 (- (string-length a) 1))
          a)))))
(define
  md/-cells
  (fn (line) (map (fn (c) (trim c)) (split (md/-strip-pipes line) "|"))))

(define
  md/-plain?
  (fn
    (line)
    (if
      (md/-blank? line)
      false
      (if
        (ct-starts-with? line "```")
        false
        (if
          (md/-heading? line)
          false
          (if
            (ct-starts-with? line "> ")
            false
            (if
              (md/-hr? line)
              false
              (if (md/-ul? line) false (if (md/-ol? line) false true)))))))))

;; ── multi-line collectors ──
(define
  md/-code
  (fn
    (lines i acc)
    (md/-code-collect
      (rest lines)
      (md/-drop (first lines) "```")
      (list)
      i
      acc)))
(define
  md/-code-collect
  (fn
    (lines lang body i acc)
    (cond
      ((= (len lines) 0)
        (md/-walk
          lines
          (+ i 1)
          (cons (mk-code (md/-id i) lang (md/-join-nl (reverse body))) acc)))
      ((= (first lines) "```")
        (md/-walk
          (rest lines)
          (+ i 1)
          (cons (mk-code (md/-id i) lang (md/-join-nl (reverse body))) acc)))
      (else
        (md/-code-collect (rest lines) lang (cons (first lines) body) i acc)))))

(define
  md/-table-body
  (fn
    (lines headers rows i acc)
    (if
      (= (len lines) 0)
      (md/-walk
        lines
        (+ i 1)
        (cons (mk-table (md/-id i) headers (reverse rows)) acc))
      (let
        ((line (first lines)))
        (if
          (md/-pipe-row? line)
          (md/-table-body
            (rest lines)
            headers
            (cons (md/-cells line) rows)
            i
            acc)
          (md/-walk
            lines
            (+ i 1)
            (cons (mk-table (md/-id i) headers (reverse rows)) acc)))))))
(define
  md/-table
  (fn
    (lines i acc)
    (md/-table-body
      (rest (rest lines))
      (md/-cells (first lines))
      (list)
      i
      acc)))

(define
  md/-list-collect
  (fn
    (lines items i acc ordered)
    (if
      (= (len lines) 0)
      (md/-walk
        lines
        (+ i 1)
        (cons (mk-list (md/-id i) ordered (reverse items)) acc))
      (let
        ((line (first lines)))
        (cond
          (ordered
            (if
              (md/-ol? line)
              (md/-list-collect
                (rest lines)
                (cons (md/-drop-ol line) items)
                i
                acc
                ordered)
              (md/-walk
                lines
                (+ i 1)
                (cons (mk-list (md/-id i) ordered (reverse items)) acc))))
          (else
            (if
              (md/-ul? line)
              (md/-list-collect
                (rest lines)
                (cons (md/-drop-ul line) items)
                i
                acc
                ordered)
              (md/-walk
                lines
                (+ i 1)
                (cons (mk-list (md/-id i) ordered (reverse items)) acc)))))))))

(define
  md/-para-collect
  (fn
    (lines parts i acc)
    (if
      (= (len lines) 0)
      (md/-walk
        lines
        (+ i 1)
        (cons (mk-text (md/-id i) (md/-join-sp (reverse parts))) acc))
      (let
        ((line (first lines)))
        (if
          (md/-plain? line)
          (md/-para-collect (rest lines) (cons line parts) i acc)
          (md/-walk
            lines
            (+ i 1)
            (cons (mk-text (md/-id i) (md/-join-sp (reverse parts))) acc)))))))

;; ── main walk ──
(define
  md/-walk
  (fn
    (lines i acc)
    (if
      (= (len lines) 0)
      (reverse acc)
      (let
        ((line (first lines)))
        (cond
          ((md/-blank? line) (md/-walk (rest lines) i acc))
          ((ct-starts-with? line "```") (md/-code lines i acc))
          ((md/-heading? line)
            (md/-walk
              (rest lines)
              (+ i 1)
              (cons (md/-heading-block line i) acc)))
          ((ct-starts-with? line "> ")
            (md/-walk
              (rest lines)
              (+ i 1)
              (cons (mk-quote (md/-id i) "" (md/-drop line "> ")) acc)))
          ((md/-hr? line)
            (md/-walk
              (rest lines)
              (+ i 1)
              (cons (mk-divider (md/-id i)) acc)))
          ((md/-table-start? lines) (md/-table lines i acc))
          ((md/-ul? line) (md/-list-collect lines (list) i acc false))
          ((md/-ol? line) (md/-list-collect lines (list) i acc true))
          (else (md/-para-collect lines (list) i acc)))))))

(define
  md/parse
  (fn (text) (md/-walk (split text (str "\n")) 0 (list))))

;; ── frontmatter (leading --- key: value --- block) ──
(define
  md/-frontmatter?
  (fn (lines) (and (> (len lines) 0) (= (first lines) "---"))))
(define
  md/-fm-end
  (fn
    (lines i)
    (cond
      ((>= i (len lines)) -1)
      ((= (nth lines i) "---") i)
      (else (md/-fm-end lines (+ i 1))))))
(define
  md/-fm-add
  (fn
    (acc line)
    (let
      ((parts (split line ":")))
      (if
        (< (len parts) 2)
        acc
        (let
          ((key (trim (first parts)))
            (val (trim (md/-join-with ":" (rest parts)))))
          (cond
            ((= key "title") (assoc acc :title val))
            ((= key "slug") (assoc acc :slug val))
            ((= key "tags")
              (assoc acc :tags (map (fn (t) (trim t)) (split val ","))))
            (else acc)))))))
(define
  md/-fm-pairs
  (fn
    (lines start end acc)
    (if
      (>= start end)
      acc
      (md/-fm-pairs
        lines
        (+ start 1)
        end
        (md/-fm-add acc (nth lines start))))))

;; ── adapter ──
(define
  md/import
  (fn
    (text doc-id)
    (let
      ((lines (split text (str "\n"))))
      (if
        (md/-frontmatter? lines)
        (let
          ((end (md/-fm-end lines 1)))
          (if
            (= end -1)
            (doc-new doc-id (md/-walk lines 0 (list)))
            (doc-with-meta
              (doc-new
                doc-id
                (md/-walk
                  (md/-drop-n lines (+ end 1))
                  0
                  (list)))
              (md/-fm-pairs lines 1 end {}))))
        (doc-new doc-id (md/-walk lines 0 (list)))))))

(define content/from-markdown md/import)
(define markdown-adapter {:export (fn (doc) (asMarkdown doc)) :import md/import})